(a) Field of the Invention
The present invention relates to thermoplastic wholly aromatic polyimide esters which have excellent dimensional stability, and more particularly to novel polyimide esters capable of being suitably used for electric and electronic parts, etc. which require excellent dimensional stability and accuracy in both flow direction (machine direction: MD) and a direction making a right angle with the flow direction (transverse direction: TD).
(b) Description of the Related Art
In recent years, thermoplastic resins having extremely small coefficients of linear expansion in MD have come to be known. These resins are a series of resins called thermotropic liquid-crystalline polymers, and some examples of such resins include the wholly aromatic copolyesters disclosed in Japanese Patent Application Laid-open No. 54-77691, etc.
The above-mentioned copolyesters have small coefficients of linear expansion in MD but are of much the same coefficients of linear expansion in TD as those of common thermoplastic resins, and are therefore hardly sufficient in dimensional stability.
Polyimide esters containing both imide bonds and ester bonds in their molecules have been well known. For example, those having excellent, high heat resistance are disclosed in U.S. Pat. No. 3,542,731, those improved in heat resistance, mechanical properties, and processabilities in Japanese Patent Application Laid-open No. 58-67725, those having high moduluses of elasticity in Japanese Patent Application Laid-open No. 55-84326, those having toughness in Japanese Patent Application Laid-open No. 58-113222, and those having high rigidity in Japanese Patent Application Laid-open No. 60-4531. However, these polyimide esters are also hardly sufficient in dimensional stability.